Dr. Monzer Kahf, a prominent Muslim economist and counselor, states that: Zakah on cash, business inventory, livestock and similar assets has a condition of Hawl (the passage of a year). It means that one lunar year (354 days) has to pass from the day you become an owner of an amount reaching the Nisab (Zakah-payable amount). If you own the Nisab and a full lunar year has passed, then subject to Zakah. This is a generous grace from Allah, Most High.

The Hawl has nothing to do with Ramadan as it begins from that mentioned date. Many people like to adjust their Hawl to Ramadan because the reward of good deeds is increased and multiplied in that month. Such adjustment is done by paying the Zakah of a partial Hawl from the date of acquiring the money until any day in Ramadan – people usually prefer the last ten days – and then they make their Hawl begins in Ramadan for all following years.
the condition of Hawl applies only to the original amount you got if it is a Nisab or more; it does not apply to any and all future increments. The Idea of Hawl serves two purposes:
1. It determines the beginning of Zakatability
2. It assures that Zakah is not taken twice in a period of 354 days.
It applies in a simple, not complicated, way. Once you are described as rich from Zakah point of view (i.e. you get to have money that reached the Nisab) then you only look at your balance at the end of the Hawl and you overlook the period in between.